Waveguide antenna with non-resonant slots



M r h 7, 1967 R. F. MORRISON, JR 3,303,467

WAVEGUIDE ANTENNA WITH NON-RESONANT SLOTS Filed March 28, 1951 v 6] 6 dH Q, [j z m INVENTOR. \9 Q Ruherfi: FlMurm'ann,Jr. 2 BY ATTOR NEYsUnited States Patent 3,308,467 WAVEGUIDE ANTENSNA WITH N ON-RESONANTLOTS This invention relate-s to waveguide antenna arrays, particularlyto waveguide antenna arrays having nonresonant slots and capable oftransmitting electromagnetic waves in narrowly defined and highlydirectional beams.

Normally, waveguide antennas of rectangular cross section have cut inone of the broad faces of the guide two rows of longitudinally spacedresonant slots. Each slot is spaced from the longitudinal axis of thebroad surface with the longitudinal axis of each slot paralleling thelongitudinal axis of the broad surface. The amount of radiation fromeach slot in the row is controlled by varying the spacing between thelongitudinal axis of each slot and the longitudinal axis of the broadsurface. The more close-1y the longitudinal axis of a slot approachesthe longitudinal axis of the broad surface, the lower the amount ofradiation therefrom. Since the slots are arranged in two rows andstaggered relative to each other, an overlapping or intersection ofslots may occur when both rows are placed at Dr extremely close to thelongitudinal axis of the broad face to obtain minimum radiation. The useof pins or stubs adjacent to the slots on the inner wall of thewave-guide has also been employed in the past as a means to control theamount of radiation from the slots. This method has proven to be timeconsuming and costly in mass production.

The directivity of the radiation pattern of slotted waveguide antennasis usually controlled by varying the longitudinal spacing between slots.For example, a spacing of one-half wavelength between resonant slotswill result in maximum radiation normal to the longitudinal axis of thewaveguide antenna. A spacing greater than one-half wavelength willresult in radiation at an angle to one side of the plane normal to thelongitudinal axis of the waveguide antenna and a spacing less thanone-half wavelength will result in radiation at an angle to the oppositeside of the plane normal to the longitudinal axis of the waveguideantenna.

A primary object of the invention is a slotted waveguide antenna havinggreat structural strength.

Another object of the invention is a microwave antenna array wherein theradiating slots of the waveguide are arranged to prevent overlapping.

Another object of the invention is a microwave antan'ce.

tenna array wherein the staggered slots in the elements of the array arearranged to avoid intersection of each other.

Another object of the invention is a waveguide antenna having novelmeans for forming the radiation pattern.

Another object of the invention is a novel means for controlling theamount of radiation of a waveguide antenna.

Another object of the invention is a waveguide antenna having noveldirectivity means incorporated therein.

Another object of the invention is the elimination of probes adjacent tothe slots for controlling the amount of radiated energy of a waveguideantenna.

The specific nature of the invention as well as other objects andadvantages thereof Will clearly appear from the following descriptionand accompanying drawings in which:

FIGURE 1 is a perspective view showing a section of a conventionalwaveguide antenna wherein the resonant slots are closely spaced withrespect to the longitudinal axis of the waveguide.

FIGURE 2 is a plan View of the slotted waveguide antenna of theinvention.

FIGURE 3 shows the radiation pattern of the waveguide antenna of FIGURE1, illustrating output in decibels in relation to the antenna axis.

FIGURE 4 is a typical plot illustrating the relationship of the slotlength to the slot conductance; and

FIGURE 5 is a perspective view showing four slotted waveguide antennasembodied in the nose of a missile.

The desired radiation pattern for the Waveguide antenna of the inventionis obtained by choosing a suitable combination of slot dimensions andlongitudinal spacing between slots. The slot spacing is given by thefollowing formula:

where d=longitudinal spacing between slot centers. \=free spacewavelength.

Ag=wavelength in the guide.

0=angle of the major lobe.

The slot size depends upon the required slot conduc- The required slotconductance is obtained from the following formula:

Gn Pn 11-1 ri-k2 PK The manner in which Pn varies with n depends uponthe desired radiation pattern. In some cases, Pn is a constant, while inothers, Pn is small near the ends of the antenna and large near thecenter. Once Gn is determined, the slot length is obtained from thecurve shown in FIGURE 4.

FIGURE 1 of the drawings shows a conventional type of'waveguide radiatorin which 1 indicates the waveguide of rectangular cross section.Radiation means comprising slots 3 and 4 are formed in the wall 2 of thewaveguide, parallel to the longitudinal axis of the wall. For certaindirectivity characteristics and radiation power, it is necessary thatthe slots be longitudinally spaced less than one-half wavelength,resulting in the waveguide wall being weakened in the areas between theadjacent ends of the opposing slots of each of the series of slots.

The present invention eliminates the possibility of positioning theslots so that overlapping at the axis can occur, for all slots of thearray of the invention are well and equidistantly spaced from thelongitudinal axis of the waveguide wall. The amount of radiation fromeach slot is controlled by the length of the slot rather than by itsdistance from the longitudinal axis of the waveguide wall.

Referring now to FIGURE 2, wherein there is shown one embodiment of thewaveguide array of the invention FIGURE 3 shows the radiation patternproduced by the slot pattern of the waveguide of FIGURE 2. However, itis to be noted that various radiation patterns can be obtained as may bedesired by selected arrangement of slot size and spacing in accordancewith the formulas listed above.

Several of the slotted waveguide antennas may be placed on the surface,or may comprise a portion thereof, of a cylinder or cone to produce aradiation pat-tern which is omnidirectional in the plane perpendicularto the axis of the cone, but highly directional in the plane containingthe axis of the cone. The number and distribution of the slottedwaveguide antennas depends upon the all-owable variation in beam angleand radiated power as the cone is rotated about its axis. The variationin beam angle is due to the fact that th cone axis and waveguide axisare not parallel. The power variation is due to interference effects anddirectivity of the individual antennas. An embodiment of the foregoingis shown in FIGURE 5 wherein f-our radiating elements 11, 12, 13 and 14are disposed at equal intervals around the conical nose 15 of a missile16. The elements 11, 12, 13 and 14 are supplied with microwave energyfrom a common source such as a transceiver 17 by means of waveguidefeeders 18, 19, 20 and 21, respectively. Accordingly, an explosivemissi-le, having an aerodynamic surface, may be provided with amicrowave antenna array conforming to the aerodynamic surface.Obviously, the antenna array is adapted to produce an omnidirectionalradiation pattern in azimuth about the longitudinal axis of the missileand inclined in elevation as desired in respect to the direction offlight of the missile.

I claim:

In an explosive missile having an aerodynamic surface, a microwaveantenna array conforming to said aerodynamic surface and producing anomnidirectional radiation pattern in azimuth about the longitudinal axisof said missile and inclined in elevation as desired in respect to thedirection of flight of said missile, said array comprising a multiple ofwaveguide radiators fixed in spaced relationship in the peripheralsurface of the nose of said missile, microwave generating means fixedwithin the said nose, each of said waveguide radiators connected to saidgenerating means by waveguide feeders, each of said waveguide radiatorshaving formed in one wall thereof two rows of microwave radiating meansin staggered relation to each other and equidistantly spaced from thelongitudinal axis of said wall, said microwav radiating means comprisingresonant slots in said wall intermediate the end of said guide andprogressively non resonant slots on each side of said resonant slotstowards the ends of said guide to form a microwave radiation beam havingits major lobe intermediate said ends, the said beam of each waveguidecontributing to form said omnidirectional radiation pattern.

References Cited by the Examiner UNITED STATES PATENTS 2,574,433 11/1951Clapp 343-771 2,648,839 8/1953 Ford et al 343-771 ELI LIEBERMAN, PrimaryExaminer.

NORMAN H. EVANS, Examiner.

R. E. BERGER, Assistant Examiner.

